Republican officials say the House can still—and very well might—sue Obama over his orders to protect as many as five million immigrants from deportation, but the fact that they chose Friday morning to file their healthcare lawsuit sent a message that they would follow through on their own threats of action. "The House will, in fact, act," Boehner insisted to reporters when he appeared outside his Capitol office to respond to Obama's immigration speech. As if to prove his point, the announcement about the Obamacare lawsuit came barely an hour later.

"That’s not the way our system of government was designed to work. If this president can get away with making his own laws, future presidents will have the ability to as well. The House has an obligation to stand up for the Constitution, and that is exactly why we are pursuing this course of action.”

Filed in the U.S. federal district court in Washington, the lawsuit challenges the Obama administration's decision to unilaterally delay implementation of the employer mandate in the 2010 law, along with cost-sharing subsidies paid to insurance companies that House Republicans allege were not appropriated by Congress. It names not the president himself but the secretaries of the Treasury Department and the Department of Health and Human Services as defendants, and it asked the court to issue an injunction against the administration. "The House has been injured, and will continue to be injured, by defendants’ unlawful actions which, among other things, usurp the House’s legislative authority," the lawsuit claims.

The legal challenge will test not only whether the president exceeded his authority but whether the House has the standing to take him to court. Legal scholars have said there is little precedent for a lawsuit by a single chamber of Congress against the president, and House GOP aides have privately acknowledged a judge could throw the challenge out before even ruling on the merits of the case.

"The fact is, this lawsuit is a bald-faced attempt to achieve what Republicans have been unable to achieve through the political process," Representative Nancy Pelosi, the House Democratic leader, said in response on Friday. "The legislative branch cannot sue simply because they disagree with the way a law passed by a different Congress has been implemented. It is clear, as one leading legal scholar put it, that this lawsuit is ‘an embarrassing loser.’"

Yet after the president's immigration move on Thursday, it is likely not the final legal salvo from House Republicans. Boehner said they hadn't decided how exactly they planned to confront the president, but his office made clear that an additional lawsuit, which would require a separate vote by the House, was under consideration.

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Russell Berman is a staff writer at The Atlantic, where he covers politics.